Acoustics Watermarking for Air ASW Systems

In the Multi-static Active Coherent (MAC) systems concept, acoustic sources and receivers are deployed over a wide area. The sources are radio command activated to transmit waveforms designed for various purposes (e.g. Continuous Wave (CW) pulses provide optimal Doppler resolution, Hyperbolic Frequency Modulated (HFM) pulses provide optimal time resolution). The “direct blast” of the transmission travels directly from source to receiver, and the target echo travels from source to target, reflects from the target, and travels from target to receiver. When a target echo is detected, the target location is calculated by associating it with a source, calculating the range (from travel time), and then calculating the target location as the intersection of the ellipse defined by that range and its direction of arrival. Increasing the tempo at which sources are fired improves target tracking. However, target echoes must be associated with sources, and the greater the number of sources, the more difficult this becomes. AOS will develop the Secure Watermarking for Identification and Tracking (SWIFT) technology, which embeds “watermark” signals on transmitted waveforms to unambiguously identify and authenticate each received waveform according to its source. In addition to a watermark, SWIFT will embed acoustic communication messages into the source waveforms, to be decoded from the direct blast by nearby friendly platforms.